1. Field of the Invention
The present invention relates to a process and apparatus for warming of suspensions or solutions of living cell substance, such as units of human blood which are frozen in a flat plastic bag and which are called hereinafter freezing samples.
2. Description of the Prior Art
According to a known process, the use of larger quantities comprising a sample mass of approximately 50-500 g and the use of samples shaped into thin plates having a layer thickness of approximately 5-10 mm is common practice in order to obtain an economical quantity of frozen living blood cells and an economical yield of cryoglobulins. When using thin plates of this type, a uniform rate of temperature change, i.e. temperature change in relation to time, can be maintained within the limits of approximately 10% for almost the entire sample mass, except for the boundary layer. In common practice, the solutions discussed in the present disclosure are filled into a plastic bag which thereafter is heatsealed and frozen in a platelike holder in a way which is known in principle.
The rate of the temperature change during the warming process should be of the same order of magnitude as during the freezing process; however, a significantly more rapid warming rate as compared to the cooling rate is aimed at. Thereby devitrification and/or recrystallization and occurrence of intracellular ice for example inside frozen cells can be prevented. In the prior art, in order to avoid during the warming process a temperature gradient having a harmful effect between the ice block and the geometrical center of the plate and the boundary layer, forced convection is impressed upon the sample inside the bag by shaking. Thereby, on one hand the heat transfer to the melting ice is increased, and on the other hand overheating of particles close to the boundary of the aqueous solution is avoided.
Up until now, the warming process of the sample is carried out as follows:
Introduction of the sample which is frozen in a plate-like bag into a water bath of e.g. 40.degree. C.; PA1 maintaining the melting sample in platelike shape during the process by means of special holders or containers, respectively; PA1 moving of the sample with a frequency of approximately 4 Hz with an amplitude of approximately 8 cm in longitudinal direction; PA1 after reaching an experimentally established predetermined time, removal of the bag from the water bath; PA1 drying of the bag provided the sample is completely thawed and proceeding of the sample to further use.
The disadvantages of this known warming process are as follows:
1. The duration of time required for thawing during which the sample has to be immersed in the water bath is highly dependent on the mass of the sample. Even small variations of the mass in relation to an established mean value which are common in practice result in significant exceeding or falling below the temperature desired after thawing, e.g. +4.degree. C. of the sample. Likewise, incomplete melting of the ice in the sample can be observed which may result in considerable damage to the quality of the material.
2. The handling of the samples can only be done by specially trained, qualified personnel as the positioning of samples frozen in the platelike bag during immersion in the water bath has to be done as rapidly as possible because the thawing process sets in immediately in full extent. The liquid occurring in the sample at this instant will deform the sample if it is not properly fixed. Rapid positioning is also important because as soon as the liquid occurs forced convection in the sample has to be started.
3. A special holder or container maintaining the sample in platelike shape is needed for the duration of the warming process. This necessitates the storage of each sample in appropriate containers beforehand which entails a considerable expenditure for each single sample or the locating of the sample in a container or holder after the sample has been introduced into the low temperature environment resulting in the well-known difficulties (such as ice formation, unintended warming of the sample, frost bites to the hands of the persons handling the sample) in particular when storing the material in liquid nitrogen as usual in medical practice.
4. The necessary drying of the sample after the thawing procedure represents additional work and loss of time. Drying of the bag is indispensable as normally ensuring handling under sterile conditions is foreseen; residues of water on the inlet and outlet connections would destroy sterility.